Described herein is a composition and method for the formation of a dielectric film using alkyl-alkoxysilacyclic compounds as a structure former precursor(s). More specifically, described herein is a composition and method for formation of a porous low dielectric constant (“low k” film or film having a dielectric constant of about 2.7 or less) film wherein the method is used to deposit the film is a chemical vapor deposition (CVD) method. The dielectric films, produced by the compositions and methods described herein, can be used, for example, as insulating layers in electronic devices.
The electronics industry utilizes dielectric materials as insulating layers between circuits and components of integrated circuits (IC) and associated electronic devices. Line dimensions are being reduced in order to increase the speed and memory storage capability of microelectronic devices (e.g., computer chips). As the line dimensions decrease, the insulating requirements for the interlayer dielectric (ILD) become much more rigorous. Shrinking the spacing requires a lower dielectric constant to minimize the RC time constant, where R is the resistance of the conductive line and C is the capacitance of the insulating dielectric interlayer. Capacitance (C) is inversely proportional to spacing and proportional to the dielectric constant (k) of the interlayer dielectric (ILD). Conventional silica (SiO2) CVD dielectric films produced from SiH4 or TEOS (Si(OCH2CH3)4, tetraethylorthosilicate) and O2 have a dielectric constant k greater than 4.0. There are several ways in which industry has attempted to produce silica-based CVD films with lower dielectric constants, the most successful being the doping of the insulating silicon oxide film with organic groups providing dielectric constants ranging from about 2.7 to about 3.5. This organosilica glass is typically deposited as a dense film (density ˜1.5 g/cm3) from an organosilicon precursor, such as a methylsilane or siloxane, and an oxidant, such as O2 or N2O. Organosilica glass will be herein be referred to as OSG. As dielectric constant or “k” values drop below 2.7 with higher device densities and smaller dimensions, the industry has exhausted most of the suitable low k compositions for dense films and has turned to various porous materials for improved insulating properties.
Patents, published applications, and publications in the field of porous ILD by CVD methods field include: EP 1 119 035 A2 and U.S. Pat. No. 6,171,945, which describe a process of depositing an OSG film from organosilicon precursors with labile groups in the presence of an oxidant such as N2O and optionally a peroxide, with subsequent removal of the labile group with a thermal anneal to provide porous OSG; U.S. Pat. Nos. 6,054,206 and 6,238,751, which teach the removal of essentially all organic groups from deposited OSG with an oxidizing anneal to obtain porous inorganic SiO2; EP 1 037 275, which describes the deposition of an hydrogenated silicon carbide film which is transformed into porous inorganic SiO2 by a subsequent treatment with an oxidizing plasma; and U.S. Pat. No. 6,312,793 B1, WO 00/24050, and a literature article Grill, A. Patel, V. Appl. Phys. Lett. (2001), 79(6), pp. 803-805, which all teach the co-deposition of a film from an organosilicon precursor and an organic compound, and subsequent thermal anneal to provide a multiphase OSG/organic film in which a portion of the polymerized organic component is retained. In the latter references, the ultimate final composition of the films indicate residual porogen and a high hydrocarbon film content of approximately 80 to 90 atomic %. Further, the final films retain the SiO2-like network, with substitution of a portion of oxygen atoms for organic groups.
A challenge, which has been recognized in the industry, is that films with lower dielectric constants typically have higher porosity, which leads to enhanced diffusion of species into the films, specifically gas phase diffusion. This increased diffusion can result in increased removal of carbon from the porous OSG film from processes such as etching of the film, plasma ashing of photoresist, and NH3 plasma treatment of copper surfaces. Carbon depletion in the OSG films can cause one or more of the following problems: an increase in the dielectric constant of the film; film etching and feature bowing during wet cleaning steps; moisture absorption into the film due to loss of hydrophobicity, pattern collapse of fine features during the wet clean steps after pattern etch and/or integration issues when depositing subsequent layers such as, without limitation, copper diffusion barriers, for example Ta/TaN or advanced Co or MnN barrier layers.
Possible solutions to one or more of these problems are to use porous OSG films with increased carbon content. A first approach is to use a porogen which results in a higher retention of Si-Methyl (Me) groups in the porous OSG layer. Unfortunately, as depicted in FIG. 1, the relationship between increasing Si-Me content typically leads to decreasing mechanical properties, thus the films with more Si-Me will negatively impact mechanical strength which is important for integration. A second approach has been to use a damage resistant porogen (DRP), such as, for example, the porogen disclosed in U.S. Pat. No. 8,753,985, which leaves additional amorphous carbon behind in the film after UV curing. In certain cases, this residual carbon does not negatively impact the dielectric constant nor the mechanical strength. It is difficult, however, to get significantly higher carbon contents in these films using the DRP.
Yet another solution proposed has been to use ethylene or methylene bridged disiloxanes of the general formula Rx(RO)3-xSi(CH2)ySiRz(OR)3-z where x=0-3, y=1 or 2, z=0-3. The use of bridged species is believed to avoid the negative impact to the mechanical by replacing bridging oxygen with a bridging carbon chain since the network connectivity will remain the same. This arises from the belief that replacing bridging oxygen with a terminal methyl group will lower mechanical strength by lowering network connectivity. In this manner one, can replace an oxygen atom with 1-2 carbon atoms to increase the atomic weight percent (%) C without lowering mechanical strength. These bridged precursors, however, generally have very high boiling points due to the increased molecular weight from having two silicon groups. The increased boiling point may negatively impact the manufacturing process by making it difficult to deliver the chemical precursor into the reaction chamber as a gas phase reagent without condensing it in the vapor delivery line or process pump exhaust.
Thus, there is a need in the art for a dielectric precursor that provides a film with increased carbon content upon deposition yet does not suffer the above-mentioned drawbacks.